1. Field of the Invention
This invention relates to hydrogenated anionic block copolymers of mono alkenyl arenes and conjugated dienes, and to articles made from such block copolymers. This invention particularly relates to hydrogenated block copolymers of styrene and butadiene or isoprene.
2. Background of the Art
The preparation of block copolymers of mono alkenyl arenes and conjugated dienes is well known. One of the first patents on linear ABA block copolymers made with styrene and butadiene is U.S. Pat. No. 3,149,182. Uses for the block copolymers include injection molding, extrusion, blow molding, adhesives, and the like. These polymers have also been used in applications such as the modification of bitumen for the production of roofs and roads. Other uses of block copolymers include the production of films, fibers, and non-woven fabrics.
One example of such a block copolymer is in U.S. Pat. No. 4,188,432 to Holden, et al. Disclosed therein are shaped articles which are resistant to attack by fatty substances consisting essentially of high impact styrene-butadiene graft copolymer or a mixture thereof with no more than about 55% styrene homopolymer. The shaped articles also include small proportions of polyethylene or polypropylene and of a block copolymer X-Y-X in which each X is a polystyrene block of about 5,000 to 10,000 molecular weight and Y is a hydrogenated polybutadiene block of 25,000 to 50,000 molecular weight.
Another example of a block copolymer is found in U.S. Pat. No. 5,705,556 to Djiauw, et al. In this reference, it is disclosed that an extrudable elastomeric composition for making elastic fibers or films can be prepared using an elastomeric block copolymer, a polyphenylene ether, a polyolefin, and a tackifying resin. The article is further described as having from 25% to 75% by weight of a block copolymer having at least two monoalkenyl arene blocks separated by a hydrogenated conjugated diene block.
It is known in the art of preparing articles from polymers using injection molding, extrusion, and fiber spinning to use processing aids to reduce undesirable properties of the polymer being used. For example, fiber lubricants having excellent stability to smoking under conditions of use at elevated temperature in the mechanical and heat treatment operation subsequent to extrusion of the fiber, is disclosed in U.S. Pat. No. 4,273,946 to Newkirk, et al.
The above referenced block copolymer and today's other conventional highly elastic block copolymers, while having many desirable properties, can be difficult to process, particularly in extrusion, molding and fiber spinning applications. For example, it is commonly practiced to use substantial amounts of polyolefins, extending oils, tackifying resin and waxes and/or other processing aids in order to extrude conventional block copolymers. These additives can be difficult to add, often lead to reductions in elastic properties and can cause undesirable processing problems such as smoking and die buildup. On the other hand, conventional block copolymers can be made with good processability, however their mechanical properties are so poor that they are not generally useful in molded and extruded articles. It would be desirable in the art of preparing molded, extruded, and spun articles from block copolymers to prepare such articles using a block copolymer that does not require as much or even any processing aids and yet has excellent elastic properties.